Isocyanato-aryl sulfochlorides are known. According to German Pat. No. 947,159 they may be obtained by phosgenating aromatic aminosulfonic acids. The disadvantage of this process lies in the need to use high-boiling solvents, such as dichlorobenzene and, in particular, nitrobenzene. Another disadvantage is the poor solubility of the aminosulfonic acids used as starting material in these solvents, even at the high reaction temperatures applied. As a result, the reaction is laborious and the yield of the isocyanato-aryl sulfochlorides obtained is unsatisfactory. This applies in particular to the production of diisocyanato-aryl sulfochlorides. In Example 3 of German Pat. No. 947,159, for example, a yield of 46% of the theoretical was obtained. Because of the disadvantages referred to above, this process has not acquired any commercial significance.
It is also known that simple aryl sulfochlorides can be obtained by sulfonating aromatic compounds, for example, with chlorosulfonic acid or with mixtures of chlorosulfonic acid and sulfuryl chloride (cf. for example, Houben-Weyl, 4th Edition, Vol. 9, pages 563 to 585). It is also known that sulfochlorides can be produced from free sulfonic acids or their salts with acid chlorides. Prior to the instant invention, these known processes have rarely been used for the manufacture of isocyanato-aryl sulfochlorides from aromatic isocyanates, and only with negative results, there are several reasons for this.
First, the sulfochlorination reaction with chlorosulfonic acid requires an excess of chlorosulfonic acid and hence, necessitates working-up in the presence of water with the result that the isocyanate groups are attacked. Second, isocyanato-sulfonic acids in the form of dimeric uretdiones have only recently become known and have proved to be extremely reactive compounds which are very difficult to handle. In addition, sulfonic acid groups react unpredictably with isocyanates at elevated temperature, with the elimination of carbon dioxide. Thus, under the conditions normally used for the production of sulfochlorides, other reactions, for example, sulfone and anhydride forming reactions and also polymerization reactions involving the isocyanate group, can be expected to take place to a considerable extent.
It is known from U.S. Pat. No. 3,686,301 that 3,5-dichlorosulfobenzoyl chloride can be obtained by reacting 3,5-disulfobenzoic acid heated to 180.degree. C. with 3 times the molar quantity of benzotrichloride. The benzotrichloride is added over a period of 3 hours and the temperature is slowly reduced to 130.degree. C. during the addition and the mixture is stirred for another hour at 130.degree. C.
It is also known (cf. German Pat. No. 574,836) that the sodium salts of aromatic sulfonic acids can be reacted with benzotrichloride to form the corresponding aromatic sulfonic acid chloride. In addition, according to this German patent, the known reaction of free carboxylic acids with benzotrichloride in the presence of zinc chloride for producing the carboxylic acid chlorides cannot be applied to free organic sulfonic acids.
Prior to the instant invention, it was unknown to react isocyanato-aryl sulfonic acid uretdiones with aromatic trihalogen methyl compounds. The misgivings expressed above also apply to this reaction, especially since it is carried out at temperatures above 100.degree. C.
It has now surprisingly been found that compounds containing aromatically bound isocyanate groups or aromatically bound carbamic acid chloride groups can also be converted particularly easily in good yields into aromatic isocyanates containing aromatically bound sulfochloride groups, providing that the starting materials are reacted successively or simultaneously with sulfonating agents and compounds containing aromatically bound trihalogen methyl groups. The expected complex secondary reactions which generally occur because of the presence of highly reactive isocyanate groups or carbamic acid chloride groups do not result. In addition, the use of the above-mentioned aromatic trihalogen methyl compounds has the advantage over the use of thionyl chloride or phosgene as the halogenating agent that no acid amide is used as catalyst. Also, in the case of low molecular weight process products, the crude product may be distilled directly without preliminary purification.